TreeView.BeforeCheck 事件

定義

命名空間:

System.Windows.Forms

組件:

System.Windows.Forms.dll

發生於選取樹狀節點選取方塊之前。

public:
 event System::Windows::Forms::TreeViewCancelEventHandler ^ BeforeCheck;

public event System.Windows.Forms.TreeViewCancelEventHandler BeforeCheck;

member this.BeforeCheck : System.Windows.Forms.TreeViewCancelEventHandler 

Public Custom Event BeforeCheck As TreeViewCancelEventHandler 

事件類型

TreeViewCancelEventHandler

範例

下列程式碼範例會在使用者變更其核取狀態時，更新 的所有子樹狀節點 TreeNode 。 此程式碼需要您具有 FormTreeView 的 ，且其 TreeNodeCollection 中具有 TreeNode 物件。 TreeNodeCollection應該有具有子節點的樹狀節點。

// Updates all child tree nodes recursively.
void CheckAllChildNodes( TreeNode^ treeNode, bool nodeChecked )
{
   IEnumerator^ myEnum = treeNode->Nodes->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      TreeNode^ node = safe_cast<TreeNode^>(myEnum->Current);
      node->Checked = nodeChecked;
      if ( node->Nodes->Count > 0 )
      {
         
         // If the current node has child nodes, call the CheckAllChildsNodes method recursively.
         this->CheckAllChildNodes( node, nodeChecked );
      }
   }
}

// NOTE   This code can be added to the BeforeCheck event handler instead of the AfterCheck event.
// After a tree node's Checked property is changed, all its child nodes are updated to the same value.
void node_AfterCheck( Object^ /*sender*/, TreeViewEventArgs^ e )
{
   // The code only executes if the user caused the checked state to change.
   if ( e->Action != TreeViewAction::Unknown )
   {
      if ( e->Node->Nodes->Count > 0 )
      {
         /* Calls the CheckAllChildNodes method, passing in the current
             Checked value of the TreeNode whose checked state changed. */
         this->CheckAllChildNodes( e->Node, e->Node->Checked );
      }
   }
}

// Updates all child tree nodes recursively.
private void CheckAllChildNodes(TreeNode treeNode, bool nodeChecked)
{
   foreach(TreeNode node in treeNode.Nodes)
   {
      node.Checked = nodeChecked;
      if(node.Nodes.Count > 0)
      {
         // If the current node has child nodes, call the CheckAllChildsNodes method recursively.
         this.CheckAllChildNodes(node, nodeChecked);
      }
   }
}

// NOTE   This code can be added to the BeforeCheck event handler instead of the AfterCheck event.
// After a tree node's Checked property is changed, all its child nodes are updated to the same value.
private void node_AfterCheck(object sender, TreeViewEventArgs e)
{
   // The code only executes if the user caused the checked state to change.
   if(e.Action != TreeViewAction.Unknown)
   {
      if(e.Node.Nodes.Count > 0)
      {
         /* Calls the CheckAllChildNodes method, passing in the current 
         Checked value of the TreeNode whose checked state changed. */
         this.CheckAllChildNodes(e.Node, e.Node.Checked);
      }
   }
}

' Updates all child tree nodes recursively.
Private Sub CheckAllChildNodes(treeNode As TreeNode, nodeChecked As Boolean)
   Dim node As TreeNode
   For Each node In  treeNode.Nodes 
      node.Checked = nodeChecked
      If node.Nodes.Count > 0 Then
         ' If the current node has child nodes, call the CheckAllChildsNodes method recursively.
         Me.CheckAllChildNodes(node, nodeChecked)
      End If
   Next node
End Sub
      
' NOTE   This code can be added to the BeforeCheck event handler instead of the AfterCheck event.
' After a tree node's Checked property is changed, all its child nodes are updated to the same value.
Private Sub node_AfterCheck(sender As Object, e As TreeViewEventArgs) Handles treeView1.AfterCheck
   ' The code only executes if the user caused the checked state to change.
   If e.Action <> TreeViewAction.Unknown Then 
      If e.Node.Nodes.Count > 0 Then
         ' Calls the CheckAllChildNodes method, passing in the current 
         ' Checked value of the TreeNode whose checked state changed. 
         Me.CheckAllChildNodes(e.Node, e.Node.Checked)
      End If
   End If
End Sub

備註

注意

TreeNode.Checked從 或 AfterCheck 事件中 BeforeCheck 設定 屬性會導致事件多次引發，而且可能會導致非預期的行為。 例如，當您遞迴更新子節點時，可能會在事件處理常式中設定 Checked 屬性，讓使用者不需要個別展開和檢查每個節點。 若要防止多次引發事件，請將邏輯新增至事件處理常式，只有在 的 TreeViewEventArgs 屬性未設定 TreeViewAction.Unknown 為 時 Action ，才會執行遞迴程式碼。

如需如何處理事件的詳細資訊，請參閱 處理和引發事件。

另請參閱

• CheckBoxes
• OnBeforeCheck(TreeViewCancelEventArgs)
• AfterCheck
• OnAfterCheck(TreeViewEventArgs)